Androgens play important roles in prostate development and two major diseases - prostate cancer and benign prostatic hyperplasia (BPH). Understanding the mechanism of androgen action may lead to new approaches of treatment and/or prevention of prostate cancer and/or BPH. This project is proposed to elucidate the cellular mechanisms of androgen action in the prostate, particularly the role of androgen-responsive gene EAF2. EAF2 stands for ELL (Eleven-Nineteen Lysine-rich Leukemia)-associated factor 2 (EAF2), a transcription elongation factor. Our lab has generated multiple observations that indicate a key role for EAF2 in androgen action and prostatic diseases. EAF2 expression was up- regulated in all assayed benign prostatic hyperplasia (BPH) nodules and down-regulated in 60-80% of advanced prostate cancers with Gleason scores of 7-10. Overexpression of EAF2 in prostate cancer cells induced apoptosis and growth inhibition in culture, as well as in xenografts. EAF2 knockout mice developed high-grade prostatic intraepithelial neoplasia (PIN). However, the mechanisms by which EAF2 suppresses prostatic cell growth and carcinogenesis remain unclear. Preliminary studies suggest that endogenous EAF2 could bind to p53 and modulate p53 function. Concurrent loss of EAF2 and p53 induced prostate cancer, whereas single knockout of EAF2 or p53 did not. Also, we generated evidence for EAF2 modulation of androgen receptor (AR) target gene PSA expression in vivo. p53 has been reported by other investigators as a modulator of AR function and is one of the most frequently deleted/mutated tumor suppressors in advanced prostate cancer specimens. Our data, together with the observations of others, led to the research hypothesis that EAF2 and p53 act synergistically in modulating tumor suppression and AR signaling in the prostate. Based on this hypothesis, we propose to complete the following 3 specific aims. Aim 1 will investigate EAF2 interaction with p53 using GST-pull down, deletion mutagenesis, siRNA knockdown, microarray and ChIP-Seq. Aim 2 will determine the role of EAF2 and p53 in AR-regulated gene expression and cell proliferation using siRNA knockdown, microarray, ChIP-Seq, and BrdU assay in LNCaP and/or EAF2-p53 knockout mouse model. Aim 3 will determine the effect and relevance of concurrent loss of EAF2 and p53 in prostate carcinogenesis using conditional p53 and EAF2 double knockout mice, shRNA knockdown in LNCaP xenograft tumor model, and clinical prostate cancer specimens. The success of this project may lead to new approaches to distinguish aggressive prostate tumors from indolent ones based on their status of EAF2, p53, and other important tumor suppressors and/or oncogenes. This project may also identify new therapeutic targets that are abnormally activated by current loss of EAF2 and p53 in prostate cancer.